MIXED FARMING systems, the largest
category of livestock system in the world, cover about 2.5 billion hectares of land, of
which 1.1 billion hectares are arable rainfed crop land, 0.2 billion hectares are
irrigated crop land and 1.2 billion hectares are grassland. Mixed farming systems produce
92% of the world's milk supply, all buffalo meat and approximately 70% of the sheep and
goat meat (Figure 3.1). About half of the meat and milk produced in this system is
produced in the OECD, Eastern Europe and the CIS, and the remainder comes from the
developing world. Over the last decade, meat production from this system grew at a rate of
about 2 percent per year and thus remains below global in demand.

Mixed farming is probably the most
benign agricultural production system from an environmental perspective because it is, at
least partially, a closed system. The waste products of one enterprise (crop residues),
which would otherwise be loaded on to the natural resource base, are used by the other
enterprise, which returns its own waste products (manure) back to the first enterprise.
Because it provides many opportunities for recycling and organic farming and for a varied,
more attractive landscape, mixed farming is the favourite system of many agriculturalists
and environmentalists.

In many situations crop and
livestock production is largely in balance with nature. There are important exceptions,
such as some mixed farming systems of the tropical highlands of Asia and Central Africa
which, partly because of overgrazing, are amongst the most eroded and degraded systems of
the world. On the other end of the development spectrum, heavy use of feed and fertilizer
in the industrial world and in some of the fast growing economies of East Asia, has led to
nutrient loading, habitat destruction and water pollution. In this context, it has to be
remembered that integrating crops and livestock neither generates new nutrients (with the
exception of nitrogen fixation by leguminous plants) nor reduces nutrient surpluses.

As rural population pressure
increases, both crop and livestock farmers need to intensify production. McIntire et
al., (1992) show that, as population pressure increases, the two activities often
become integrated. Traditional soil protection techniques, in particular the long fallow
periods which protected against erosion and allowed soil nutrients to recharge, are no
longer possible (Kjekshus, 1977). If farmers cannot resort to external inputs, the
integration of livestock and crop activities represents their main opportunity for
intensification. Mixed farming has therefore become the basis for modern agriculture.
Mixed farming systems provide farmers with an opportunity to diversify risk from single
crop production, to use labour more efficiently, to have a source of cash for purchasing
farm inputs and to add value to crops or crop by-products. Combining crops and livestock
also has the potential to maintain ecosystem function and health and help prevent
agricultural systems from becoming too brittle, or over connected, by promoting greater
biodiversity, and therefore increased capability to absorb shocks to the natural resource
base (Holling, 1995).

Environmentally, mixed farming
systems:

 maintain soil fertility by recycling soil
nutrients and allowing the introduction and use of rotations between various crops and
forage legumes and trees, or for land to remain fallow and grasses and shrubs to become
reestablished;

 make the best use of crop
residues. When they are not used as feed, stalks may be incorporated directly into the
soil, where, for some time, they act as a nitrogen trap, exacerbating deficiencies. In the
tropical semi-arid areas, termite action results in loss of nutrients before the next
cropping season. Burning, the other alternative, increases carbon dioxide emissions; and

 allow intensified farming,
with less dependence on natural resources and preserving more biodiversity than would be
the case if food demands were to be met by crop and livestock activities undertaken in
isolation.

Under different sets of pressures
and opportunities, several developments are possible, depending on resource endowment and
market access. Initially, and if market opportunities open up, the symbiosis between crops
and livestock can intensify (Christiaensen et al., 1995 and Box 3.1), and
the nutrient balance can be maintained. This chapter's case study (Box 3.6) on the
long term evolution of a mixed farming system in the semi-arid regions of Kenya
illustrates this development.

Box 3.1
Population pressure and the evolution of the cassava-livestock system in sub-Saharan
Africa.

POPULATION PRESSURE and the
evolution of the cassava-livestock system in sub-Saharan Africa. A comparative analysis of
cassava-livestock interactions in six countries, covering seven regions in sub-Saharan
Africa, clearly shows that as population intensity increases, crop-livestock interactions
intensify as organic fertilizer and the use of cassava as a livestock feed gain
importance. For example, in the densely populated areas of Nigeria, between 77 and 100
percent of the animals were fed farm-grown cassava, whereas in the sparsely populated
areas of Zaire and Tanzania, this varied between 8 and 50 percent. Livestock thus help to
conserve a better nutrient balance within the system, and reduce the threat of nutrient
loss.

Source: Christiaensen et al., 1995.

If pressure increases further,
crop-livestock systems can separate into specialized crop or livestock activities. If
there are no improved market opportunities, which is the case in many developing
countries, and as human population pressures continue, the arable land part of the system
will experience increased rates of nutrient depletion (and therefore flora and fauna
biodiversity loss) and soil erosion. This can, in turn, lead to a downward spiral of
mono-culture with lower quality food crops, increased under-nutrition and famine (Cleaver
and Schreiber, 1994). This development path is illustrated in this chapter's case study on
Rwanda in Central Africa (Box 3.4).

However, if urban incomes rise, more
market opportunities open up and farmers become more integrated into the market economy,
allowing them to specialize, take advantage of economies of scale and develop greater
levels of expertise. Finally, under very strong demand, and often encouraged by input or
price subsidies such as exist in many developed countries and in the fast growing
economies of East Asia, excessive importation of nutrients can lead to soil and water
tables being overloaded with nitrogen or phosphorus. The case study on Brittany in France
illustrates this condition (Box 3.7).

The challenge for the mixed farm
sector will therefore be to maintain a nutrient and energy equilibrium through
crop-livestock integration and at the same time allow sustainable productivity growth. The
mixed farming system, more than any other production system, operates under a wide range
of environmental and economic conditions and requires regional solutions and practices.
However, there is one overriding criteria in determining the size and nature of the
system's impact on the environment, and this is the nutrient balance. This balance is
determined by the nutrients (N. P and K) brought into the farming systems by inorganic
fertilizer, feed, nitrogen fixed by leguminous plants and transfer from grazing areas
outside the farm, and the amounts exported in animal products or lost from the land to the
air or groundwater. A positive balance of nutrients will have a completely different
effect (and will require different measures) than a nutrient deficient system. In this
analysis, the mixed farming systems are classified either as nutrient deficient systems,
which occur mainly in the developing world, or as nutrient surplus systems, mostly found
in the industrialized world and increasingly in the fast growing economies of East Asia.

The mixed farming systems of the
developing world contain about 67 percent of the cattle and 64 percent of the small
ruminants of the world. Throughout the world, animal numbers are growing in the mixed
farming system, most rapidly in the humid/sub-humid regions (Annex 2). Sheep and
goat numbers show the fastest growth rates in the humid/sub-humid region, underlining how
human population pressure is reducing farm size and access to and use of resources.

Irrigated mixed farming systems have
shown the greatest increase in productivity, particularly in the humid regions of Asia.
This is clearly a result of the strong growth in demand for animal products and better
access to feed resources and other types of infrastructure in Asia. Milk production is
important, particularly in south Asian countries, due to the growing demand in the region
and the favorable policies that many governments have created for the dairy sector.
Although the growth of dairy production can place more pressure on land resources, it can
also increase the use of crop by-products which in turn improves nutrient recycling and,
if of high quality, can diminish methane production.

There is a considerable range of
positive and negative interactions between livestock and the environment within the
different sub-systems. These interactions can affect land quality in its physical (soil
erosion) and chemical properties (soil fertility), the use of nonrenewable resources, such
as fossil fuels and fertilizer, and the conservation of agricultural (plant and animal)
biodiversity. They are detailed below.

Soil erosion is
probably the most pervasive form of land degradation in the developing world. Erosion
rates are particular high in Asia, Africa and South America where they average 30 to 40
tons/ha/year, compared with an average soil formation of 1 ton per ha/per year (Pimental et
al., 1995). In Africa, 60 percent of soil erosion damage occurs in the semi-arid and
dry sub-humid regions where cropping and livestock co-exist (Thomas and Middleton, 1994),
with strong interlocking factors of cropping, fuelwood collection and grazing.

Soil erosion is even more damaging
on sloping lands. Poorly managed sloping terraces under crops and degraded rangelands can
lose up to 100 MT/ha/year. Conversely, well managed pasture land loses 7 MT/ha/year or
less and well managed forest land losses range from 0-10 MT/ha/year. Bojo and Cassells
(1995) quantified these losses in the degraded Ethiopian Highlands (Box 3.2). Their
results showed the effect of including pastures in those environments as a means of
reducing erosion.

The
nutrient export results from the use of dung an crop residues as fuel.

The Gross Discounted Cumulative Loss
captures the cumulative nature of the land degradation, in which each year's erosion and
nutrient loss is followed by another adding layers of losses and hence cost on top of each
other

Source: Bojo and Cassells, 1995.

Soil fertility.
Livestock play a significant role in maintaining soil fertility. In partially closed mixed
farming systems, livestock can replenish a substantial share of soil nutrients, and
therefore reduce the need for inorganic fertilizer, with corresponding savings for farmers
in terms of cash outlay, for the country in foreign exchange, and for the world in
non-renewable resources. The total value of this contribution is not known, although
approximate figures are given by Jansen and de Wit (1996) for the irrigated mixed farming
systems of Asia. Assuming manure production of about 1 ton dry material per year per
Tropical Livestock Unit1, and an effective availability2 of 15
percent of the nutrients in the case of stall fed and half that amount for grazing
animals, the amount of nutrients under stall fed conditions is about 8 kg N and 6 kg P per
year per TLU.

1 A Tropical Livestock Unit (TLU) is
an animal unit used to aggregate different classes of livestock. One TLU equals an animal
of 250 kg liveweight.

2 The balance is lost
through evaporation, leaching and, in many arid areas, through use as fuel.

Under those assumptions, livestock
in the mixed irrigated farming system can supply between 2 and 10 percent of the nitrogen
requirements for rice, and about 40 to 120 percent of the requirements for phosphorus in
cassava (Table 3.1).

As can be clearly seen from Table
3.1, nitrogen is the most depleted nutrient, with the amount lost varying, depending
upon the technology used in collection, storing and application practices. How farmers
approach these three factors largely determines the effectiveness of the recycling process
and therefore provides an avenue for intervention. As shown, stall feeding significantly
increases the amount of nutrients available from manure.

To demonstrate the importance of
these contributions, an estimate was made of the amount of fertilizer that would be
required to replace the manure that is used in the irrigated system of the humid tropics.
The value of this is estimated to be between US$ 700 to US$ 850 million per year,
depending on various assumptions (Table 3.2).

The economic benefits of improved
soil structure as a result of adding soil organic matter from manure are more difficult to
estimate. Adding manure to the soil increases cation exchange capacity, and improves soil
physical conditions by increasing the water-holding capacity and improving soil structure
stability. When adding the manure output from pigs and ruminants together, livestock may
contribute up to 35% of the soil organic matter requirements. This is a crucial
contribution because this is the only avenue available to many farmers for improving soil
organic matter.

Non-renewable resources.
Draught animal power, in addition to other economic benefits, provides an important source
of energy in the mixed farming systems of the world and helps to reduce dependence on
nonrenewable fuel resources. In developing countries, animal power is used to cultivate
about 52 percent of the 480 million hectares of cropland (FAO, 1994). Draught animals
provide between 25 to 64 percent of the energy needed for cultivation in the irrigated
systems of the world. Worldwide 300 million draught animals are used in small-scale
agriculture, while 30 million tractors would be needed to make the same contribution. This
is equivalent to an US$ 200-300 billion investment in tractors plus a $5 billion annual
fuel cost. Assuming that approximately 50 percent of the arable land is cultivated in the
world's irrigated areas with draught animal power, complete replacement by tractors would
require annually 888 million litres of diesel at a cost of US$ 222 million, and US$ 429
million for depreciation of the equipment (Jansen and de Wit, 1996).

Assuming rice yields of 4 tons per
ha, and cassava yields of 10 tons Per ha

Source: Jansen and de Wit, 1996.

The value of animal manure for
cooking fuel is more controversial. Dung cakes are the main source of household energy for
millions of poor households in the developing world. It is often argued that using dung
for fuel removes soil nutrients and therefore carries high opportunity costs (Mearns,
1996). However nitrogen is the only major nutrient that is lost because the remaining ash
is high in phosphorus and potassium.

Biodiversity. In mixed
farming systems, livestock-environment interactions can be a key focal point. As human
population pressures increase, some types of wildlife or plant diversity can be lost while
other types of biodiversity may actually increase. Reid et al. (1995) demonstrate
how the number of tree, bird and mammal species changes as human use of the resource base
intensifies (Figure 3.2).

These results are important for
demonstrating the dynamic nature of ecological systems. They also show that man's
agricultural activities must be balanced with the environment's capacity to sustain them.

An often overlooked component of
biodiversity is soil micro-flora and fauna. Arthropods, with 90 percent of all species,
dominate biodiversity (Pimental et al., 1992). For example, in a New York alfalfa
"ecosystem" Pimental et al., (1992) reported 600 species of above ground
arthropods. Livestock and manure have a beneficial effect on this biodiversity. For
example, in mixed farms in Japan, the species diversity of the micro-fauna under grass
more than doubled when manure was added to the land (Kitazawa and Kitazawa, 1980).

In forest and communal grazing
areas, adjacent to mixed farming areas, plant and animal biodiversity is decreasing
because of over-grazing. There are many examples quoted in the literature confirming this
trend, for example, in Syria, Rajastan, and West Africa. It is not clear, though, whether
these are irreversible, long term changes. For example, Thomas and Middleton (1994) report
that no systematic pattern of vegetation change could be detected in a 27 year vegetation
survey of 77 villages in the Sudan. However, wildlife biodiversity is disturbed if land is
fragmented and river sides are cultivated. Finally, the mixed farming areas of the world
contain the main centres of domestic animal genetic resources (local livestock breeds) of
the world. Urgent steps to safeguard that future capital are proposed in Chapter 5.